Assuming we're okay with killing our prisoners, I don't see what's so wrong with death by firing squad. It's cheap, fast, painless, and can be carried out by people who have little training. If you don't want to see the condemned person's discomfort, you could still sedate them just as they do with lethal injection. Maybe death by firing squad doesn't make for as exciting theatrics as the complex and methodical procedures of lethal injection, but I'm sure we could come up with something for the audience. And if that's unpalatable for lawmakers... Maybe we should reconsider the whole thing.